import java.util.StringTokenizer;


class P438_39643 {

	public static void main(String[] args) {
		
		String line = readLn();
		
		while (line != null) {
			process(line);
			
			line = readLn();
		}
		
	}
	
	private static void process(String line) {
		StringTokenizer st = new StringTokenizer(line);
		
		double x1, x2, x3, y1, y2, y3;
		
		
		
		x1 = new Double(st.nextToken()).doubleValue();
		y1 = new Double(st.nextToken()).doubleValue();
		x2 = new Double(st.nextToken()).doubleValue();
		y2 = new Double(st.nextToken()).doubleValue();
		x3 = new Double(st.nextToken()).doubleValue();
		y3 = new Double(st.nextToken()).doubleValue();
		
//		float ma = (y2 - y1) / (x2 - x1);
//		float mb = (y3 - y2) / (x3 - x2);
//		
//		float x = (ma * mb * (y1 - y3) + mb * (x1 + x2) - ma * (x2 + x3) ) / 2 * (mb - ma);
//		
//		float y = ma * (x - x1) + y1;
//		
//		float r = Math.sqrt(((x - x1) * (x - x1)) + ((y - y1) *(y - y1)));
//		
		double pi = 3.141592653589793;
//		
//		float value = 2 * pi * r;
//		
//		System.out.println(value);
		

		 double p=(x1-x2);
		 double q=(x2-x3);
		 double r=(x3-x1);

		 double p1=(y1-y2);
		 double q1=(y2-y3);
		 double r1=(y3-y1);

		 double a=Math.sqrt(Math.pow(p,2)+Math.pow(p1,2));
		 double b=Math.sqrt(Math.pow(q,2)+Math.pow(q1,2));
		 double c=Math.sqrt(Math.pow(r,2)+Math.pow(r1,2));

		 double s=(a+b+c)/2.0;
		 p=(s-a);
		 q=(s-b);
		 r=(s-c);

		 double L=Math.sqrt(s*p*q*r);

		 r=(a*b*c)/L;
		 r=r/4;

		 double C=2*pi*r; 
		 
		 C = C * 100;
		 
		 long Clong = (long) Math.round(C);
		 
		 String answer = Long.toString((Clong / 100)) + ".";
		 
		 long remainder = Clong % 100;
		 
		 if (remainder == 0) {
			 answer += "00";
		 } else {
			 if (remainder < 10) {
				 answer += "0" + remainder;
			 } else {
				 answer += remainder;
			 }
		 }

		 System.out.println(answer);
		 
	}

	static String readLn() {
		String newLine = System.getProperty("line.separator");
		StringBuffer buffer = new StringBuffer();
		int car = -1;
		try {
			car = System.in.read();
			while ((car > 0) && (car != newLine.charAt(0))) {
				buffer.append((char) car);
				car = System.in.read();
			}
			if (car == newLine.charAt(0))
				System.in.skip(newLine.length() - 1);
		} catch (java.io.IOException e) {
			return (null);
		}
		if ((car < 0) && (buffer.length() == 0))
			return (null);
		return (buffer.toString()).trim();
	}
	
}
